Incidence, toxin gene profiling, antimicrobial susceptibility, and genetic diversity of Bacillus cereus isolated from quick-frozen food in China

Bacillus cereus is a well-known foodborne pathogen around the world and can be found in a variety of foods. However, few studies have been conducted to evaluate the risk of B. cereus in quick-frozen food in China. Hence, we investigated the prevalence, antimicrobial susceptibility, presence of toxin genes, biofilm formation ability, and genetic polymorphisms of B. cereus isolated from quick-frozen food in China. Of the 598 samples collected from 39 cities, 193 were contaminated by B. cereus. Regarding the distribution of toxin genes, 116 out of 224 B. cereus isolates possessed hblA/C/D, nheA/B/C, and cytK-2. The positive rates for nheA, nheB, and nheC were very high (100.0%, 100.0%, and 88.8%, respectively). In contrast, only nine strains contained the cereulide synthetase encoding gene cesB. Of all the isolates, 94.2% were identified as multiple antibiotic-resistant strains. Genetic polymorphism analyses revealed that 224 strains could be classified into 161 sequence types (STs), of which 92 were new STs. In summary, our study demonstrated that quick-frozen foods were highly contaminated with B. cereus, and this may pose a potential hazard to public health.